This application focuses on understanding how aging affects the function of pancreatic beta cells and how this contributes to the development of type 2 diabetes (T2D). T2D is related to aging and is partly characterized by dysfunctional insulin secretion. The important interaction between age and altered beta cell function is further illustrated by its continued decline as diabetes progresses coupled with an inability of the beta cell population to control hyperglycemia by enhanced proliferation. Such lack of response to mitogenic stimuli is considered cellular senescence and has been linked to the expression of p16Ink4a. Adult beta cells are heterogeneous both in expression of p16Ink4a and function, raising the possibility that beta cell function is related to age and that at any point in the adult there are cells at different stages: immature, mature and senescent. However, such transition remains to be studied. Our preliminary data suggest the existence of a senescent subpopulation of beta cells that accumulates with age, expresses a unique senescence signature and displays functional decline. Our hypothesis is that beta cells at various life stages have different markers (such as IGF-1R) and functional characteristics, and that both age and environmental factors can shift the composition of the population. We will study well-defined mouse models to develop exciting new tools and insights that will be tested then on human islets. Our goal is to identify the subpopulations of beta cells at different life stages, understand their aging and determine whether manipulations can alter beta cell functional longevity. Specific Aim 1. To identify markers of aged beta cells, the functional changes that characterize this life cycle stage and whether IGF-1R can mediate these changes. The hypothesis is that beta cells go through different life stages and as the animal ages the older subpopulation of cells is enriched, enabling the identification of aging markers, functional features and potential mechanisms. This aim will identify markers associated with aged beta cells to derive a specific senescence gene signature (with emphasis on cell surface markers) and explore a mechanistic role of IGF-1R in their aging. Specific Aim 2. To analyze whether the heterogeneity in glucose responsiveness of adult beta cells is determined by their lifecycle stage. The hypothesis is that the known functional heterogeneity of beta cells reflects the different stages of their lifecycle. Senescent and non-senescent subpopulations of beta cells will be collected, their function analyzed and the effects of aged cells upon the function of neighboring younger beta cells evaluated. Specific Aim 3. To test how the heterogeneity determined by aging changes in response to insulin resistance in the absence or presence of hyperglycemia. We hypothesize that insulin resistant states that precede T2D accelerate aging of the beta cells thus accelerating the development of disease. This aim will test the effects of increased metabolic demand and its rescue upon beta cell aging. These studies should provide insights into how beta cells respond to insulin resistance, impaired glucose tolerance and T2D.